Myford Super 7 Tachometer

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About time I got around to this, I've had the bits for over 6 months ;-)
My first step was to fit the sensor and magnet somewhere that would give true RPM even in back-gear.

My Super 7 isn't standard, but for one that is fitting a cylindrical magnet in one of the holes in the standard Super 7 gear and making the bracket reach far enough back to place the sensor behind the gear would work. I've tested function with a cylindrical magnet at 90 degrees to the sensor and it works fine.

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I am assuming that you have a variable speed controller and that you need finer control than simple marked positions on a dial. I have the standard Super 7 with three belt speeds and it provides sufficient rpm range to get my jobs done. So my question is what advantage do you get in fine tuning the spindle speed?

Well-Known Member

I am assuming that you have a variable speed controller and that you need finer control than simple marked positions on a dial. I have the standard Super 7 with three belt speeds and it provides sufficient rpm range to get my jobs done. So my question is what advantage do you get in fine tuning the spindle speed?

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Theoretically you have TWO belt speeds from a 1440 rpm motor which gives 14(?) speeds.

As other readers might be aware, I also have a SiegC4 which- apart from a readout- actually gives LESS low speed performance.

I did have a converter and 3 phase motor on the Super7B but there wasn't a fat lot in it.

What continues to intrigue me was how Martin Cleeve bought half a Myford ML7 and fitted TWO motors to it. One was a full blown 1Horse power affair whilst the other was the more conventional fractional motor.

Of course I have a perfectly adequate stroboscope from motor car tuning days and simply scratch my head when I still have to guess the speed of the table on my milling machine.

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Looking at the wiring diagram I realised that only 4 out of 5 connections were used and that by wiring two sockets the same (Socket-Display, 1-1, 2-2, 3-3 and 4-5 I could use two identical 4 pin connectors for power and sensor and it wouldn't matter which plug mated with which socket.
I was also going to build an enclosure but realised with two 5mm spacers the sockets would mount to the back cover with safe internal clearance for wiring.

I'll probably make a mounting bezel from aluminium soon but I've a few other things more pressing to get done that the rpm readout will really help with ;-)

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I am assuming that you have a variable speed controller and that you need finer control than simple marked positions on a dial.

Click to expand...

I have a Siemens Vector Drive VFD running a 0.75Kw motor.
The final drive belt stays on the pulleys next to top speed.
The primary drive belt stays on the high speed pulleys.
This gives me a usable 0-3000rpm with enough torque to tap Stainless up to M8 on the Jog button at a couple of rpm, I'll confirm actual speed once I mount the tachometer read out ;-)

So, in carrying out 95% + of my turning at one ratio it's going to be a great help to be able to read spindle nose rpm directly, I refer to my workbook and set the rpm I determined best for the job last time I was doing something the same or similar.
When I use back gear for heavy jobs I still get direct rpm reference.
I suppose you may not need or want VFD or rpm read out if you never refer to the recommended cutting data for your tools or materials and your chosen jobs aren't demanding enough to make variable speed and direct read out convenient tools to have.

So my question is what advantage do you get in fine tuning the spindle speed?

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It is possible to tune chip formation, and on some jobs tune out resonance, with a small change in speed where changing pulley will take you out of the sweet spot for the job.

I made a batch of 50 Titanium pins last month with a short section around 6.5mm and a 50mm length at 3.25mm. I cut the 3.25mm section using a roller box and the sweet spot for chip formation and clearance fell in a very narrow speed range, next time I do the job I'll note the rpm on the job's page in my log book.

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I am working on a CNC lathe and a second CNC mill and I already have a CNC milling machine, but I will not be getting rid of my manual lathe or manual milling machines any time soon, what happens when you need a simple washer, bush, nut or bolt? Or even a part to repair your CNC when it breaks? ;-)

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Good point as a friend with a CNC machine shop business also keeps a manual lathe which he uses for fine tuning or correction of parts that are off spec.

Mostly I make a simple washer, bush, nut, bolt or a part for broken machines. Even with DRO on my Bridgeport I'll often start it up without the read outs to fly cut a flat surface. Simple is good for my needs.

Well-Known Member

Im a bit late here responding but for future reference you can find prox switches specifically designed to count gear teeth spinning by. At least you could 30 years ago when i was working on machines using them. I wouldn't be surprised if modern general purpose prox switches could do this today.

You just need access to a suitable gear and a scalable readout device.